Coating of screws

ABSTRACT

A method of making a screw threaded fastener (1, 10) for fixing cladding to a building includes the steps of applying a mastic covering (5, 15) to a screw threaded portion (4, 13) of the fastener, and applying a non-sticky protective coating (6, 16) to the outside of the mastic covering (5, 15) so as to prevent the fasteners (1, 10) from sticking together during handling and packaging of the same. Preferably the protective coating (6, 16) is as coating of a waxy substance and is applied to the outside of the mastic covering (5, 15) by means of a dipping or spraying process or operation. The fasteners are then easy to use and form a water-tight, moisture and vapor-proof seal with respect to their supports or substrates. The waxy coating (16) may also be applied to the drill point (12) so as to act as a lubricant during driving of the fastener.

FIELD OF THE INVENTION

The present invention relates generally to fasteners and a method ofmaking the same, and more particularly to a screw-threaded fastener tobe used in connection with securing metal cladding to buildingframeworks, and a method of making such a fastener.

BACKGROUND OF THE INVENTION

Many modern industrial buildings are constructed by first constructing astrong steel framework and then cladding the same with thin profiledmetal sheets so as to form the walls and roof.

It is also common practice to add insulation material to the walls androof of the building so as to conserve energy and to help to maintain acomfortable environment within the building. This added insulation isusually sandwiched between the roof or walls and the framework as theroof and walls are connected to the underlying framework by usingself-drilling, self-tapping screw-threaded fasteners. A typical buildinghas many thousands of such fasteners.

Inside a typical air-conditioned building there is usually a smallpositive pressure which forces warm moist air from the interior of thebuilding along the screw threads and into the wall and roof voids, aswell as into the insulation material. The temperature outside of theroof void and the temperature gradient within the roof void varyaccording to location, the time of year and the time of day but,frequently, the void will be cooler than the inside of the building.

The warm air from the building therefore cools within the roof and wallvoids and consequently moisture condenses. This condensation typicallyreacts with chemicals present within the insulation material so as toform an acid which subsequently attacks the fastenings. This chemical orcorrosive attack can lead to very severe corrosive deterioration of thefastenings and the structural integrity of the associated structuralframework and network. Alternatively, condensation can accumulate andsaturate the insulation so as to reduce its thermal efficiency. In themost severe cases, the condensation flows back into the building andgives the impression of being leakage.

Corrosion is a frequent cause for concern in connection with mechanicalfastenings, particularly corrosion caused by the use of dissimilarmetals which are widely used in the metal building constructionindustry. The most severe situation occurs when a conductingelectrolyte, such as, for example, acidified water, accumulates at ajunction defined between the fastening and the metal framework orprofiled sheet. The resulting corrosion is caused by means of a galvanicreaction which occurs between the dissimilar metals.

At present a cadmium coating is often applied to the underlying fastenerand this coating acts as both an anti-corrosion coating and as a solidlubricant. However, this is not preferred from a pollution standpointand therefore a zinc anti-corrosion coating is preferred. This type ofcoating, however, tends to ball up and jam the drilling and self-tappingeffect of the fastener.

In order to overcome the problems of corrosion we have coated aproportion of the screw threads, and sometimes the drill point, of sucha fastener with a mastic coating which acts as a sealant at the junctionof the screw and the metal framework or profiled sheet so as to preventthe ingress of moist air and which also serves as a protective coatingagainst galvanic corrosion of the fastener. The mastic coating isapplied to the fasteners either by means of dipping them point firstinto a supply of the mastic or by rolling a band of mastic around thescrew thread.

Having applied the mastic, the screws are then rapidly passed into aninfra-red conveyor oven so as to cure an outer layer thereof and form askin, and are subsequently cooled by means of an air blast or are waterquenched.

If the fasteners are coated and packed without performance of thispreliminary curing step they stick together and form an unusable mass.This process is very sensitive to temperature and the curing time. Inaddition since the resin is partially cured at the skin or surface,curing or cross-linking of the remainder of the mastic continues veryslowly and this means that the product has only a limited shelf-life.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention a method of makinga screw threaded fastener includes the steps of applying a masticcovering to a screw threaded portion of the fastener, and applying anon-sticky protective coating to the outside of the mastic covering soas to prevent the fasteners from sticking together during handling andpackaging of the same.

Preferably the protective coating comprises a coating of a waxysubstance and is applied to the outside of the mastic covering by meansof dipping or spraying processes.

According to a second aspect of this invention, a screw threadedfastener includes a mastic covering disposed around a screw threadedportion of the fastener, and a waxy coating covering the outside of themastic covering so as to prevent the fastener from sticking to similarfasteners during handling and packaging of the fasteners.

Preferably the waxy coating is impervious to the transmission ofsolvents from the mastic covering to the atmosphere, the transmission ofgas such as, for example, oxygen which reacts with the mastic covering,and to the transmission of ultra violet light. In this way the waxcoating not only prevents fasteners from sticking to one another butalso protects the mastic covering from deterioration and thus increasesthe shelf-life of the fasteners.

According to a third aspect of this invention a screw threaded fastenerincludes a drill point and a waxy material coating the drill point.

We have found that the application of a waxy coating material to thedrill point of the fastener acts as a lubricant as the drill point ofthe fastener enters an underlying purlin and, even if the fastener iszinc coated, the insertion of the fastener is facilitated.

Preferably the waxy material has a melting point above 50° C. and it isparticularly preferred that its melting point is above 60° C. Preferablythe waxy material also has a low shrinkage factor so that it does notshrink and crack so as to undesirably expose the mastic coveringdisposed therebeneath. Examples of suitable waxy materials aremicrocrystalline waxes, and a blend of microcrystalline wax and a waxknown as Epolene. Such a material adheres very well to the drill pointand screw thread and resists being displaced by means of a centrifugalaction so that it acts as a lubricant throughout the fastener drivingoperation.

Preferably the mastic covering is a non-curing type of mastic such as,for example, a general purpose butyl rubber based sealant or a siliconebased sealant such as, for example, that sold under the name Silite. Itmay also be of the curing type such as, for example, an epoxy basedplastic resin material sold under the Registered Trade Mark TENABOND.The mastic materials or compositions may include corrosion resistingfillers such as, for example, zinc, aluminum or magnesium for protectingsteel against galvanic action by means of providing a sacrificial anodetherefor.

The mastic covering may be applied in generally the same way as thatdescribed above. Alternatively, it is applied by means of a dipping orspraying process or operation but preferably the fastener is insertedinto a mold and then the mastic material is injected into the moldcavity and is formed around the fastener.

In the case of small diameter fasteners including a drill point fordrilling through thick metal it is desirable that the drill point flutesare not blocked or obstructed by means of the mastic covering so as tomaintain the drilling performance. In the past this has been achieved bymeans of rolling the mastic material onto the fastener. However, bymeans of a preferred method developed in accordance with this invention,the drill point of the fastener is initially coated with a preliminarywaxy coating before the mastic covering is applied thereto. The masticmaterial does not adhere to the preliminary waxy layer, but only adheresto those parts of the fastener which are not wax coated. The waxdisposed upon the drill point of the fastener can then either be left inposition or it can be removed by means of dipping the drill point of thefinished product into a hot oil bath so as to render the point clean. Anouter waxy layer is then applied over the mastic covering and the drillpoint. This method avoids rolling the mastic material onto the fastenerand avoids drill point contamination during application of the masticmaterial. The preliminary waxy coating and/or the outer waxy layer actsas a fusible lubricant during driving of the fastener.

The proposed invention requires less complicated mechanization, there isno need for an accurately controlled conveyor oven, and thus theequipment is more compact and less difficult to control.

Preferably the or each waxy coating is applied with the waxy materialbeing heated to a temperature level above its melting point. Preferablythe fasteners are subjected to a water or forced air quench process oroperation after the or each application of the waxy material so as toensure that the material has cooled sufficiently so as to form a hardcoating before adjacent fasteners come into contact with one another.Multiple layers of mastic material may be built up one on top of theother, or different materials may be located at different locationsalong the fastener by repeating the mastic application steps outlinedabove.

BRIEF DESCRIPTION OF THE DRAWINGS

Particular examples of screw threaded fasteners in accordance with thisinvention will now be described with reference to the accompanyingdrawings, in which like reference characters designate like orcorresponding parts throughout the several views, and wherein:

FIG. 1 is a partially sectioned side elevation of a first embodiment ofthe present invention;

FIG. 2 is a partially sectioned side elevation of a second embodiment ofthe present invention;

FIG. 3 is a partially sectioned side elevation of a third embodiment ofthe present invention; and

FIG. 4 is a partially sectioned side elevation of a fourth embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT

In accordance with the first embodiment of the present invention afixing screw 1 has a domed head 2, a pointed self-drilling point 3 and ascrew-threaded portion 4. Such screws are typically used in connectionwith clamping plates so as to secure insulating material to a thinunderlying metal sheet. The lower portion of the screw thread 4 anddrill point 3 are dipped at room temperature into a mastic material suchas, for example, a general purpose butyl sealant type ID152 marketed byInduseal Developments. This provides a mastic coating 5 around thedrilling point 3 and the lower portion of thread 4 of the screw 1. Thescrews are subsequently dipped within a microcrystalline wax type 180 MHmanufactured by Witco Corp. of USA, and distributed by Eggar, of Theale,Berkshire, U.K. having 2% of a modifier wax known as Epolene C16 or NN34manufactured by Eastman Kodak Products Inc. added to it. The wax isretained at a temperature of 120° C. The screws are removed from the waxbath and dipped into cold water so as to cool the wax to a temperaturelevel which is below its melting point of 60° C. so as to form arelatively hardened non-sticky coating 6 over the outside of the masticcovering 5. Typically the fasteners 1 are conveyed by means of a beltconveyor which engages the fasteners beneath their heads 2 and leadsthem successively through a bath containing the mastic material, a bathcontaining the molten wax and the water quench.

The second example of a screw threaded fastener developed in accordancewith this invention is designated by means of the reference character 10and includes a hexagonal head 11, a drill point 12 and a screw thread13. The basic fastener is of the type that is sold by ITW Buildex undertheir registered trade mark TEKS. The drill point 12 is dipped into afirst bath containing molten wax. After removal from the bath thefastener 10 is cooled by means of an air quench so as to cool the waxadhering to the drill point 12 so as to provide a solid wax coating 14upon the drill point 12. The fastener 10 is then dipped into a bath ofmastic material and withdrawn. The mastic material does not adhere tothe wax coating 14 but does adhere to the non-coated lower portions ofthe screw thread 13 so as to provide a band of mastic material 15 uponthe lower screw threaded portion of the fastener. The preliminary waxcoating 14 may be optionally be removed by means of dipping the drillpoint 12 into a hot oil bath. The fastener 10 is subsequently dippedinto a molten bath of micro-crystalline wax type 180 MH having 2% of amodifier wax known as Epolene added to it. The wax is maintained at atemperature of 120° C. This provides a wax coating around the outside ofthe mastic covering 15 and the preliminary wax 14 where this isretained. This outer wax coating is cooled to a temperature level whichis below its melting point by means of an air or water quench. Again thefastener will typically be conveyed by means of a conveyor belt which isengaged beneath its head 11 while it is engaged between the variousbaths and quenches. The preliminary wax coating 14 and/or wax coating 16typically melt a the drill point 12 of the fastener drills through asteel purlin, the wax coatings serving as a lubricant during thedrilling process.

The third example in accordance with the present invention is generallysimilar to the second example but, in this example the drill point 12 issubsequently dipped into a hot oil bath so as to remove both thepreliminary wax coating 14 and the outer wax coating 16 from the drillpoint in order to leave the drill point 12 and its flutes completelyfree from wax.

The fourth example of the present invention is shown in FIG. 4 andcomprises a fastener 10 similar to that in the second and thirdexamples. The fastener is zinc plated so as to enhance its corrosionresistance. The drill point 12 and the lowest threaded portions of thescrew thread 13 are coated with wax 16 by being dipped into a moltenbath of microcrystalline wax type 180MH and 2% of Epolene which ismaintained at a temperature of 120° C. Upon subsequent cooling by meansof an air or water quench the wax 16 solidifies so as to form a solidcoating upon the fastener.

Upon driving a fastener in accordance with the first, second and fourthexamples of the present invention, the heat generated by means of thetip of the fastener during penetration of an underlying purlin melts thewa 16 and the melted wax therefore acts as a lubricant for thesubsequent self tapping operation of the fastener. This facilitates thedriving of the fastener and overcomes any tendency of a zinc coating to"ball up" and resist the driving of the fastener. This type of wax 16also clings tightly to the fastener so that it is not displaced by meansof the centrifugal action developed during the drilling operation.

Obviously, many modifications and variations of the present inventionare possible in light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims, the presentinvention may be practiced otherwise than as specifically describedherein.

I claim:
 1. A screw threaded fastener, comprising:a screw threadedportion defined upon a shank of said fastener; an uncured, tacky masticcovering disposed around said screw threaded portion of said fastenerfor providing corrosion-prevention and sealant properties to saidfastener when said fasten is threadedly engaged within a substrate; anda waxy coating covering said uncured, tacky mastic disposed upon saidscrew threaded portion of said fastener so as to prevent said fastenerfrom sticking to similar fasteners during handling and packaging of saidfasteners by rendering outer peripheral portions of said fastenersnon-tacky and for preventing deterioration of said uncured, tacky masticcovering.
 2. A fastener according to claim 1, wherein said waxy coatingis substantially impervious to the transmission of solvents from themastic to the atmosphere, the transmission of gas such as oxygen whichreacts with said mastic, and to the transmission of ultra violet light.3. A fastener according to claim 1, wherein said mastic includes acorrosion resisting filler.
 4. A fastener according to claim 3, whereinsaid corrosion resisting filler is selected from a group consisting ofzinc, aluminium and magnesium.
 5. A fastener according to claim 1,wherein said waxy material has a melting point above 50° C.
 6. Afastener according to claim 1, wherein said waxy material comprises amicrocrystalline wax.
 7. A fastener according to claim 1, wherein saidwaxy material has a melting point above 60° C.
 8. A fastener as setforth in claim 1, wherein said mastic covering comprises a non-curingtype mastic.
 9. A fastener as set forth in claim 8, wherein saidnon-curing type mastic comprises a butyl rubber based sealant.
 10. Afastener as set forth in claim 8, wherein said non-curing type masticcomprises a silicon based sealant.
 11. A fastener as set forth in claim1, wherein said mastic covering comprises a curing-type mastic.
 12. Afastener as set froth in claim 11, wherein said curing-type masticcomprises an epoxy based plastic resin material.